Photomask blank, photomask, and method of manufacture

ABSTRACT

A photomask blank comprising a multilayer film including at least four layers of different compositions, wherein the interface between the layers is moderately graded in composition; a phase shift mask blank comprising a phase shift film of at least two layers including a surface layer of a composition based on a zirconium silicide compound and a substrate adjacent layer of a composition based on a molybdenum silicide compound, and a further layer between one layer and another layer of a different composition, the further layer having a composition moderately graded from that of the one layer to that of the other layer; a phase shift mask blank comprising a phase shift film including a plurality of layers containing a metal and silicon in different compositional ratios which are stacked in such order that a layer having a higher etching rate is on the substrate side and a layer having a lower etching rate is on the surface side. The invention provides a photomask blank, typically a phase shift mask blank, which satisfies optical properties such as transmittance, reflectance and refractive index at an exposure wavelength of interest, and has an etched pattern with a minimal line edge roughness, and a photomask, typically a phase shift mask obtained therefrom.

CROSS REFERENCE PARAGRAPH

This application is a Divisional of co-pending application Ser. No.10/811,924, filed on Mar. 30, 2004, the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. § 120. This application also claims priority to JP2003-093712, JP 2003-093936 and JP 2003-094321 filed in Japan on Mar.31, 2003. The entire contents of which are hereby incorporated byreference and for which priority is claimed under 35 U.S.C. § 119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photomask blanks and photomasks for usein the microfabrication of semiconductor integrated circuits or thelike, and methods of manufacturing the same. It also relates to phaseshift mask blanks, phase shift masks, and methods of manufacturing thesame. More particularly, it relates to halftone phase shift mask blanksand phase shift masks which can attenuate the intensity of exposurewavelength light with a phase shift film, and methods of manufacturingthe same.

2. Prior Art

Photomasks are used in a broad range of applications, including themanufacture of semiconductor integrated circuit (IC), large-scaleintegration (LSI) and VLSI chips. They are basically constructed bystarting with a photomask blank comprising a transparent substrate and alight-shielding film made primarily of chromium thereon and processingthe light-shielding film by photolithography using UV radiation orelectron beams for thereby forming a desired pattern in the film. Themarket demand for ever higher levels of integration in semiconductorintegrated circuits has led to a rapid reduction in the minimum featuresize of photomask patterns. Such miniaturization has been achieved inpart by the use of shorter wavelength exposure light. Although exposureusing shorter wavelength light does improve resolution, it hasundesirable effects, such as reducing the focal depth, lowering processstability and adversely impacting product yield.

One pattern transfer technique that has been effective for resolvingsuch problems is phase shifting. This involves the use of a phase shiftmask as the mask for transferring microscopic circuit patterns.

As shown in accompanying FIGS. 10A and 10B, a phase shift mask(typically, halftone phase shift mask) is generally composed of asubstrate on which a phase shift film has been patterned. The mask hasboth exposed substrate areas (first light-transmitting areas) “a” onwhich there is no phase shift film, and phase shifters (secondlight-transmitting areas) “b” that form a pattern region on the mask.The phase shift mask improves the contrast of a transferred image byproviding, as shown in FIG. 10B, a phase difference of 180 degreesbetween light passing through the pattern region and light passingthrough the non-pattern region, and utilizing the destructiveinterference of light at the boundary regions of the pattern to set thelight intensity in the areas of interference to zero. The use of phaseshifting also makes it possible to increase the focal depth at thenecessary resolution. Hence, compared with a conventional mask having anordinary light-shielding pattern such as chromium film, the phase shiftmask can improve resolution and increase the margin of the exposureprocess.

For practical purposes, such phase shift masks can be broadlycategorized, according to the light-transmitting characteristics of thephase shifter, as either completely transmitting phase shift masks orhalftone phase shift masks. Completely transmitting phase shift masksare masks in which the phase shifter has the same light transmittance asthe substrate, and which are thus transparent to light at the exposurewavelength. In halftone phase shift masks, the phase shifter has a lighttransmittance that ranges from about several percent to several tens ofpercent the transmittance of exposed substrate areas.

FIG. 1 shows the basic structure of a halftone phase shift mask blank,and FIG. 2 shows the basic structure of a halftone phase shift mask. Thehalftone phase shift mask blank shown in FIG. 1 includes a transparentsubstrate 1 and a halftone phase shift film 2 formed over thesubstantially entire surface of the substrate 1. The halftone phaseshift mask shown in FIG. 2 is arrived at by patterning the phase shiftfilm 2 of the blank and includes phase shifters 2 a which form thepattern regions of the mask and exposed substrate areas 1 a on whichthere is no phase shift film. Exposure light that has passed through thephase shifter 2 a phase-shifted relative to exposure light that haspassed through the exposed substrate area 1 a. The transmittance of thephase shifter 2 a is selected such that exposure light which has passedthrough the phase shifter 2 a has too low an intensity to sensitize theresist on the substrate to which the pattern is being transferred.Accordingly, the phase shifter 2 a functions to substantially shield outthe exposure light.

Halftone phase shift masks of the above type encompass halftone phaseshift masks of the single-layer type which are simple in structure andeasy to manufacture. Single-layer halftone phase shift masks known tothe art include those described in JP-A 7-140635 which have a phaseshifting film composed of a molybdenum silicide material such as MoSiOor MoSiON.

These phase shift masks are manufactured from phase shift mask blanks.It is important for the phase shift mask blanks to exhibit a distinctetched cross-sectional geometry and low defectiveness during maskpattern formation while satisfying optical properties such astransmittance, reflectance and refractive index to the exposurewavelength of interest.

Phase shift films in such phase shift mask blanks are generallydeposited by sputtering. For the deposition, a metal silicide target istypically used which is prepared by mixing a metal and silicon in such acompositional ratio that a desired transmittance is obtainable afterdeposition, and sintering the mixture. The phase shift film thusdeposited has a constant compositional ratio of silicon to metal in adepth direction of the film.

In the aforementioned single-layer halftone phase shift mask, however,the adjustment of optical properties to desired values dictates acertain film composition. It is then difficult to produce a phase shiftfilm that can satisfy other desired properties as well.

To avoid this problem, a phase shift multilayer film has been proposedcomprising a plurality of layers including a layer satisfying opticalproperties and a layer satisfying other properties such as chemicalresistance. However, the phase shift film comprising a plurality oflayers has a problem of exacerbated line edge roughness because stepsare frequently formed in sidewalls of an etched pattern during patternformation.

Aside from the phase shift films mentioned above, a similar problemarises where a plurality of layers having different compositions arestacked to provide one function, for example, in the case of areflection type photomask having a reflective film formed by stackingalternate layers of different compositions.

Particularly when a phase shift mask is manufactured from a phase shiftmask blank, the phase shift film is typically patterned by reactive ionetching (RIE). When a layer having a constant composition of elements ina depth direction thereof is subjected to RIE, etching proceeds not onlyin a vertical direction toward the substrate, but also in a lateraldirection. Then at the end of etching, the boundary between theetched-away portion and the retained phase shift film portion isinclined in cross section. When exposure is made through a mask havingan inclined boundary geometry, the contrast of the mask pattern at theboundary becomes blurred. Only a low contrast is provided upon exposureof a very fine pattern.

SUMMARY OF THE INVENTION

An object of the invention is to provide a photomask blank, typically aphase shift mask blank, which affords a photomask that satisfies opticalproperties such as transmittance, reflectance and refractive index at anexposure wavelength of interest, and has an etched pattern with aminimal line edge roughness, that is, a photomask having an improvedetched cross-sectional geometry upon mask pattern formation; aphotomask, typically a phase shift mask obtained therefrom; and methodsof manufacturing the photomask blank and the photomask. A further objectis to provide a phase shift mask blank which exhibits goodperpendicularity in etched cross-sectional geometry upon mask patternformation by reactive ion etching (RIE); a phase shift mask obtainedtherefrom; and methods of manufacturing the phase shift mask blank andthe phase shift mask.

In one aspect, the invention pertains to a photomask blank comprising asubstrate and a multilayer film thereon including at least four layerswhose composition is different between adjacent layers. We have foundthat a photomask blank and a photomask using the same in which a maskpattern having a minimal line edge roughness can be formed are obtainedwhen the interface of each layer with an adjacent layer is moderatelygraded in composition.

In another aspect, the invention pertains to a phase shift mask blankcomprising a transparent substrate and a phase shift film of at leasttwo layers thereon. We have found that a phase shift mask blank and aphase shift mask using the same which have an improved etchedcross-sectional geometry upon mask pattern formation while satisfyingoptical properties are obtained when the phase shift film includes asurface layer of a composition based on a zirconium silicide compound, asubstrate adjacent layer of a composition based on a molybdenum silicidecompound, and at least one layer of a moderately graded compositiontherebetween.

We found that a combination of a zirconium silicide compound coatingwith a molybdenum silicide compound coating is effective as a layeredconfiguration having good chemical resistance and minimized steps inetched cross-section. However, a restrictive compositional range ofzirconium silicide compound coating and molybdenum silicide compoundcoating is required to eliminates steps in etched cross-section. Thatis, the ratio [Zr]/[Mo] of zirconium concentration [Zr] to molybdenumconcentration [Mo] must fall in the range between 0.7 and 1.3. Thislimits the freedom of design in positively improving the cross-sectionalgeometry of an etched pattern (the inclination angle of sidewall). It isdesired to solve this problem.

We have discovered that when the compositions of zirconium silicidecompound coating and molybdenum silicide compound coating arecontinuously varied, a phase shift film is obtained which develops nosteps in etched cross-section, and has improved chemical resistance andan optimum etched cross-sectional geometry, especially an optimuminclination angle.

In a further aspect, the invention pertains to a phase shift mask blankcomprising a substrate which is transparent to exposure light and aphase shift film thereon. We have discovered that when the phase shiftfilm includes a plurality of layers containing a metal and silicon indifferent compositional ratios and the layers are stacked in such orderthat a layer having a higher etching rate is on the substrate side and alayer having a lower etching rate is on the surface side, a phase shiftmask blank which exhibits good perpendicularity in etchedcross-sectional geometry upon mask pattern formation by etching,especially reactive ion etching (RIE) is obtained; that a phase shiftmask using the same has improved perpendicularity in etchedcross-sectional geometry.

We have further discovered that the phase shift mask blank ismanufactured by using a sputtering system capable of simultaneouslycausing at least two targets to produce electric discharges, andsputtering a combination of at least two metal silicide targets, or acombination of at least one metal silicide target with a metal target ora silicon target or both, thereby depositing layers on a substrate whichis transparent to exposure light, until a phase shift film is formed.

In a first embodiment, the present invention provides a photomask blank,a photomask, and a method of manufacturing a photomask blank, as setforth below.

[1] A photomask blank comprising a substrate and a multilayer filmthereon including at least four layers of different compositions,wherein the interface between the layers is moderately graded incomposition.

[2] The photomask blank of [1] wherein said multilayer film includeslayers composed mainly of compounds of metal silicide with oxygen and/ornitrogen.

[3] The photomask blank of [1] or [2] wherein said multilayer filmincludes at least one layer composed mainly of molybdenum silicideoxynitride.

[4] The photomask blank of [1] to [3] wherein said multilayer film is aphase shift film, said blank further comprising a chromium baselight-shielding film or a chromium base antireflection film or alaminate film having stacked at least one chromium base light-shieldingfilm and at least one chromium base antireflection film, formed on saidmultilayer film.

[5] A method for manufacturing the photomask blank of any one of [1] to[4], comprising

sputter-depositing layers on the substrate using a sputtering depositionsystem equipped with a plurality of targets of different compositions,across which electric powers are applied for sputtering, and graduallychanging a combination of sputtering powers across the targets inproximity to the interface between layers, thereby depositing aplurality of layers of different compositions.

[6] The method of [5] wherein the plurality of targets comprise a metalsilicide target and a silicon target.

[7] The method of [5] wherein the plurality of targets comprise a metaltarget and a silicon target.

[8] The method of [5] to [7] wherein the step of gradually changing acombination of sputtering powers across the targets in proximity to theinterface between layers continues for a power grading time period whichis at least 10% of a time period required to complete deposition of eachlayer.

[9] A photomask fabricated by patterning the multilayer film of thephotomask blank of any one of [1] to [4].

In the first embodiment of the invention, a photomask blank ofconfiguration having stacked a plurality of layers of differentcompositions can minimize the line edge roughness incurred when a maskpattern is formed in the multilayer film by etching.

More particularly, in a photomask blank comprising a multilayer filmincluding at least four layers of different compositions on a substrate,the interface of each layer with an adjacent layer is moderately gradedin composition. This ensures that when the multilayer film is patternedto fabricate a photomask, the line edge roughness of the mask pattern isminimized.

Particularly when a phase shift film is formed by the multilayer film,and a chromium base light-shielding film or a chromium baseantireflection film or a laminate film having stacked at least one layerof each of these films is formed on the phase shift film, these filmscooperate to enable more precise patterning, fully complying withfurther miniaturization and integration of semiconductor integratedcircuits.

In a second embodiment, the present invention provides a phase shiftmask blank, a phase shift mask, and a method of manufacturing a phaseshift mask blank, as set forth below.

[10] A phase shift mask blank comprising a transparent substrate and aphase shift film of at least two layers thereon,

said phase shift film having a composition based on a zirconium silicidecompound on a surface side and a composition based on a molybdenumsilicide compound on a substrate side,

said phase shift film including a first layer, a second adjacent layerof a different composition, and a third layer disposed between the firstand second layers and having a composition moderately graded from thecomposition of the first layer to the composition of the second layer.

[11] The phase shift mask blank of [10] wherein an intermediate layer isdisposed between a surface layer of a composition based on a zirconiumsilicide compound and a substrate-adjacent layer of a composition basedon a molybdenum silicide compound, said intermediate layer having acomposition moderately graded from the composition of the surface layerto the composition of the substrate-adjacent layer.

[12] The phase shift mask blank of [10] or [11] wherein a surface layerof a composition based on a zirconium silicide compound is a coatingcomposed mainly of a compound of zirconium silicide with oxygen and/ornitrogen and a substrate-adjacent layer of a composition based on amolybdenum silicide compound is a coating composed mainly of a compoundof molybdenum silicide with oxygen and/or nitrogen.

[13] The phase shift mask blank of [10] to [12], further comprising achromium base light-shielding film or a chromium base antireflectionfilm or a laminate film having stacked at least one chromium baselight-shielding film and at least one chromium base antireflection film,formed on said phase shift film.

[14] A method for manufacturing the phase shift mask blank of any one of[10] to [13], comprising

sputter-depositing layers on the substrate by using a sputteringdeposition system comprising a molybdenum silicide target, a zirconiumsilicide target and optionally a silicon target in a chamber, feeding asputtering gas containing at least oxygen and/or nitrogen, and applyingelectric powers across the targets for sputtering, and

changing a combination of sputtering powers across the targets, therebyforming the phase shift film having a graded composition.

[15] A phase shift mask fabricated by patterning the phase shift film ofthe phase shift mask blank of any one of [10] to [13].

In the second embodiment, the above-described construction enables tomanufacture a phase shift mask which is improved in etchedcross-sectional geometry upon mask pattern formation.

More particularly, a phase shift mask blank comprising a phase shiftfilm of at least two layers on a transparent substrate, and a phaseshift mask obtained therefrom, satisfy optical properties and areimproved in etched cross-sectional geometry upon mask pattern formationwhen the phase shift film includes a surface layer of a compositionbased on a zirconium silicide compound, a substrate adjacent layer of acomposition based on a molybdenum silicide compound, and at least onelayer of a moderately graded composition disposed therebetween.

Particularly when a chromium base light-shielding film or a chromiumbase antireflection film or a laminate film having stacked at least onelayer of each of these films is formed on the phase shift film, thesefilms cooperate to enable more precise patterning, fully complying withfurther miniaturization and integration of semiconductor integratedcircuits.

In a third embodiment, the present invention provides a phase shift maskblank, a phase shift mask, and methods of manufacturing the same, as setforth below.

[16] A phase shift mask blank comprising a substrate which istransparent to exposure light and a phase shift film thereon, said phaseshift film having one side contacting the substrate and a surface sideremote therefrom,

said phase shift film comprising a plurality of layers containing ametal and silicon in different compositional ratios which are stacked insuch order that a layer having a higher etching rate is on the substrateside and a layer having a lower etching rate is on the surface side.

[17] The phase shift mask blank of [16] wherein said phase shift filmcomprises one of metal silicide oxide, metal silicide nitride, metalsilicide oxynitride, metal silicide oxycarbide, metal silicide nitridecarbide and metal silicide oxide nitride carbide.

[18] The phase shift mask blank of [16] or [17] wherein said metal ismolybdenum.

[19] The phase shift mask blank of [18] wherein in said phase shiftfilm, the plurality of layers are stacked such that the compositionalratio of silicon to molybdenum increases from the substrate side to thesurface side.

[20] The phase shift mask blank of [16] to [19] wherein a phasedifference distribution in a substrate plane at the wavelength of lightused for exposure has a center value of 180±10 degrees, and atransmittance distribution in a substrate plane has a center value of 3to 40%.

[21] The phase shift mask blank of [20] wherein the phase differencedistribution in a substrate plane at the wavelength of light used forexposure is within ±2.0 degrees relative to its center value, and thetransmittance distribution in a substrate plane is within ±0.15%relative to its center value.

[22] A method for manufacturing the phase shift mask blank of [16],comprising using a sputtering system capable of simultaneously causingat least two targets to produce electric discharges, and

sputtering a combination of at least two metal silicide targets, or acombination of at least one metal silicide target with a metal target ora silicon target or both, thereby depositing layers on the substrate toform the phase shift film.

[23] The method of [22] wherein the sputtering is reactive sputteringusing a reactive gas, and said phase shift film comprises one of metalsilicide oxide, metal silicide nitride, metal silicide oxynitride, metalsilicide oxycarbide, metal silicide nitride carbide and metal silicideoxide nitride carbide.

[24] The method of [22] or [23] wherein said metal is molybdenum.

[25] The method of [24] wherein in said phase shift film, the pluralityof layers are stacked such that the compositional ratio of silicon tomolybdenum increases from the substrate side to the surface side.

[26] A phase shift mask fabricated by patterning the phase shift film ofthe phase shift mask blank of any one of [16] to [21].

[27] A method for manufacturing a phase shift mask, comprising the stepsof forming a resist film pattern on the phase shift film of the phaseshift mask blank of any one of [16] to [21] by lithography; etching awaythose portions of the phase shift film which are not covered with theresist film; and removing the resist film.

In the third embodiment, a phase shift mask blank exhibits goodperpendicularity in etched cross-sectional geometry upon mask patternformation by etching, especially reactive ion etching (RIE). Thisenables more precise patterning, fully complying with furtherminiaturization and integration of semiconductor integrated circuits.

More particularly, the third embodiment pertains to a phase shift maskblank comprising a phase shift film on a substrate which is transparentto exposure light. When the phase shift film includes a plurality oflayers containing a metal and silicon in different compositional ratiosand the layers are stacked in such order that a layer having a higheretching rate is on the substrate side and a layer having a lower etchingrate is on the surface side as viewed from the substrate side to thesurface side of the phase shift film, the phase shift mask blankexhibits good perpendicularity in etched cross-sectional geometry uponmask pattern formation by etching, especially reactive ion etching(RIE). A phase shift mask using the same has improved perpendicularityin etched cross-sectional geometry. This enables more precisepatterning, fully complying with further miniaturization and integrationof semiconductor integrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a phase shift mask blank accordingto the first and second embodiments of the invention.

FIG. 2 is a cross-sectional view of a phase shift mask according to thefirst and second embodiments of the invention.

FIG. 3 is a cross-sectional view of a phase shift mask blank accordingto the third embodiment of the invention.

FIG. 4 is a cross-sectional view of a phase shift mask according to thethird embodiment of the invention.

FIG. 5 is a cross-sectional view of a phase shift mask blank having achromium base light-shielding film according to one embodiment of theinvention.

FIG. 6 is a cross-sectional view of a phase shift mask blank having achromium base light-shielding film and a chromium base antireflectionfilm according to another embodiment of the invention.

FIG. 7 is a cross-sectional view of a phase shift mask blank accordingto a further embodiment of the invention.

FIG. 8 schematically illustrates a method of manufacturing a phase shiftmask, FIG. 8A showing a configuration having a resist film as formed,FIG. 8B showing a patterned resist film, FIG. 8C showing a configurationafter etching, and FIG. 8D showing a configuration with the resist filmremoved.

FIG. 9 is a cross-sectional view of a phase shift mask according to astill further embodiment of the invention.

FIGS. 10A and 10B illustrate the operating principle of a halftone phaseshift mask, FIG. 10B being an enlarged view of region X in FIG. 10A.

FIG. 11 schematically illustrates a dc sputtering system used inExamples 1-7 and Comparative Examples 1-4.

FIG. 12 illustrates the structure and compositional transition of amultilayer film in the first embodiment of the invention.

FIG. 13 is a cross-sectional view showing steps in an etched pattern inthe second embodiment of the invention.

FIG. 14 is a cross-sectional view showing an etched pattern in thesecond embodiment of the invention.

FIG. 15 schematically illustrates a sputtering system used in Example 8and Comparative Example 5.

FIG. 16 is a diagram showing the composition in depth direction of aphase shift mask blank obtained in Example 8.

FIG. 17 is a diagram showing the composition in depth direction of aphase shift mask blank obtained in Comparative Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

The first embodiment of the invention pertains to a photomask blankcomprising a multilayer film of at least four layers formed on asubstrate. The substrate may be a substrate which is transmissive toexposure light such as quartz and CaF₂ or a high flatness substratehaving a coefficient of thermal expansion of up to 1 ppm/° C.

The multilayer film may be either a phase shift film or a film having anoptical function such as a reflective film or semi-transmissive film. Inan embodiment wherein the multilayer film is a phase shift film, asshown in FIG. 1, a phase shift film (in this embodiment, a phase shiftmultilayer film) 2 composed of metal silicide compounds is deposited ona substrate 1. A phase shift mask is obtained by patterning the phaseshift film of the phase shift mask blank. The phase shift mask haspatterned phase shifters 2 as shown in FIG. 2, wherein firstlight-transmitting areas (exposed substrate areas) 1 a are definedbetween the patterned phase shifters and second light-transmitting areas2 a are provided by the patterned phase shifters.

The preferred phase shift mask blank has formed on a transparentsubstrate a phase shift film which is deposited by a reactive sputteringprocess using a sputtering gas containing an oxygen source gas and/ornitrogen source gas and formed of an oxide, nitride or oxynitride ofmetal silicide, has a transmittance to exposure light of severalpercents to several tens of percents, specifically about 3 to about 40%,and provides a phase difference of 180±5 degrees between light passingthrough the phase shifter and light passing through only the transparentsubstrate.

Molybdenum silicide is desirable as a metal silicide target because adense, highly pure target is obtainable. Desirably, the phase shift filmincludes at least one layer composed mainly of a molybdenum silicidecompound, especially molybdenum silicide oxynitride. Also desirable is afilm having alternately stacked layers of oxide, nitride or oxynitrideof molybdenum silicide and layers of oxide, nitride or oxynitride ofsilicon. In the event the multilayer film of the first embodiment isused as a laminate film for reflective film or the like, it is desirableto configure such that layers having different compositions of Si and Moare stacked in order.

In the first embodiment, the multilayer film includes at least fourlayers. With less than four layers, line edge roughness cannot be fullyreduced even if the composition and/or compositional ratio at the layerinterface is graded. The upper limit on the number of layers may beselected as appropriate and is usually up to 200 layers, especially upto 100 layers, though not critical.

In the first embodiment, the respective layers have differentcompositions and the interface between the layers is moderately gradedin composition. The term “different compositions” encompasses asituation in which layers are composed of different constituent elementsand a situation in which layers are composed of the same constituentelements in different compositional ratios. The term “moderately gradedcomposition” between two adjacent layers means that there may be eithera continuous or stepwise transition from the composition of one layer tothe composition of the other layer. In the latter case, the interfacemay have at least 5 steps, especially 10 to 50 steps of compositionaltransition.

It is preferred that as shown in FIG. 12, a graded region 7 ofmoderately graded composition has a thickness d, which is at least 10%of a thickness D of a single layer coating 6 whose composition hastransitioned through the graded region 7, inclusive of the thickness dof the graded region 7, that is, d/D>0.1. The upper limit of d/D may bedetermined as appropriate, and is usually d/D<1, especially d/D=0.5. Ifd/D<0.1, there is a possibility that line edge roughness becomesdeteriorated. It is noted that the thickness D is preferably 3 to 600 Å,especially 10 to 300 Å. The total layer thickness of the multilayer film5 is preferably 30 to 2,000 Å.

The method of preparing the multilayer film is described in furtherdetail. First, a plurality of targets of various compositions areprovided in a single sputtering chamber. For example, a metal silicidetarget such as molybdenum silicide is combined with a silicon target, ora metal target such as molybdenum is combined with a silicon target.

For one layer, an electric discharge may be induced to only one targetfor sputtering, or electric discharges may be induced to a plurality oftargets at the same time for sputtering whereby film constituentssputtered from the respective targets are deposited in a combinedfashion (generally referred to as co-sputtering). At this point, thesubstrate is desirably rotated about its axis so that the filmconstituents from the respective targets are uniformly mixed. A desiredfilm composition is obtained by adjusting the powers of electricdischarges applied across the respective targets.

When a multilayer film is deposited by sputtering a plurality oftargets, the step of gradually changing a combination of electric powersapplied across the targets in proximity to the interface between layerscontinues for a power grading time period which is preferably at least10%, more preferably 20 to 50% of a time period required to completedeposition of each layer.

The multilayer film is prepared using the deposition system mentionedjust above. Adjustment is done such that the electric discharge poweracross each target is gradually altered from a certain time prior to thecompletion of deposition of one layer until the composition of the nextlayer is reached. This results in a structure in which the compositionand/or compositional ratio is gradually and moderately graded inproximity to the interface between layers.

Such a compositionally graded layer is obtainable by adjusting theelectric discharge powers across the targets. By continuously changingthe electric discharge powers across the targets, a graded layer whosecomposition varies substantially continuously is obtained. By stepwiseor intermittently changing the electric discharge powers across thetargets, a graded layer whose composition varies stepwise is obtained.

Specifically, when it is desired to deposit a layer of molybdenumsilicide oxynitride (MoSiON), reactive sputtering is preferably carriedout using molybdenum silicide as the target and a sputtering gascontaining nitrogen and oxygen gases as well as argon gas.

The same applies when use is made of oxide or nitride of molybdenumsilicide or another metal (e.g., zirconium) instead of molybdenum.

In this regard, the composition of oxide, nitride or oxynitride (oxidenitride) of metal silicide is preferably selected as appropriate fromthe range: Me (metal such as Mo, Zr)=more than 0 at % to 25 at %,preferably 0.2 to 25 at %, Si=10 to 33 at %, O=0 to 67 at %, and N=0 to57 at %.

More specifically, for the oxide of molybdenum silicide (MoSiO), acomposition: Mo=more than 0 at % to 25 at %, Si=10 to 33 at %, and O=33to 67 at % is preferred; for the nitride of molybdenum silicide (MoSiN),a composition: Mo=more than 0 at % to 25 at %, Si=10 to 42 at %, andN=33 to 58 at % is preferred; for the oxynitride of molybdenum silicide(MoSiON), a composition: Mo=0.2 to 25 at %, Si=10 to 57 at %, O=1 to 60at %, and N=6 to 57 at % is preferred. In the case of silicon oxide,nitride or oxynitride, the above-mentioned composition wherein Mo=0 at %is preferred.

In another embodiment wherein the laminate film is composed of metalcoatings and is provided with a function of reflective film, forexample, metals selected from Mo, Zr, Ti, Al, Au, Cu, Ag, Cr, Ni, Co,Pd, Pt, Si, etc. may be used in any desired combination. Elementalmetals may be stacked, or alloys containing 1 to 50 at % of anothermetal may be stacked in combination. Inter alia, a combination of Mowith Si is preferred. In this case, elements Mo and Si may be separatelystacked; alternatively, Mo alloy coatings containing 1 to 50 at % ofanother metal element and Si alloy coatings containing 1 to 50 at % ofanother metal element may be separately stacked.

In the first embodiment, the photomask is arrived at by patterning themultilayer film of the photomask blank prepared as described above.

Specifically, when a phase shift mask as shown in FIG. 2 is fabricated,a process involving forming a phase shift film (phase shift multilayerfilm in this embodiment) 2 on a substrate 1 as described above, thenforming a resist film 13 thereon (FIG. 8A), patterning the resist film13 by lithography (FIG. 8B), etching the phase shift film 2 (FIG. 8C),and thereafter, removing the resist film 13 (FIG. 8D) may be employed.Coating and patterning (exposure and development) of resist film,etching and removal of resist film may be performed by well-knownmethods.

Second Embodiment

The second embodiment of the invention pertains to a phase shift maskblank comprising a phase shift film 2 formed on a transparent substrate1 which is transmissive to exposure light such as quartz and CaF₂, asshown in FIG. 1. The phase shift film includes at least two layers, asurface layer of a composition based on a zirconium silicide compoundand a layer disposed adjacent to the substrate of a composition based ona molybdenum silicide compound, the composition being moderately gradedbetween the layers. A phase shift mask is obtained by patterning thephase shift film of the phase shift mask blank. The phase shift mask haspatterned phase shifters 2 as shown in FIG. 2, wherein firstlight-transmitting areas (exposed substrate areas) 1 a are definedbetween the patterned phase shifters and second light-transmitting areas2 a are provided by the patterned phase shifters.

The layer of a zirconium silicide compound-based composition is disposedon the surface side of the phase shift film for improving chemicalresistance and the layer of a molybdenum silicide compound-basedcomposition is disposed adjacent to the substrate for providing thedesired optical properties.

In this embodiment, as the zirconium concentration of the zirconiumsilicide compound-based layer decreases, a more amount of side etchingoccurs in this surface layer upon dry etching. Inversely, as thezirconium concentration increases, a less amount of side etching occursin this surface layer. For example, where an etched cross-sectionalgeometry is inclined divergent toward the surface, the inclination canbe compensated for by increasing the zirconium concentration of thesurface layer. Then the cross-sectional geometry is corrected to aperpendicular one. Since the composition is moderately graded from thesurface layer toward the substrate, no steps are formed in the etchedcross-sectional geometry.

It is desired that the zirconium concentration [Zr] of the surface layerwhere the zirconium concentration becomes the highest divided by themolybdenum concentration [Mo] of the substrate adjacent layer where themolybdenum concentration becomes the highest be 0.1 to 2, that is, themolar ratio [Zr]/[Mo] be in the range between 0.1 and 2, more desirablybetween 0.2 and 1.5.

The zirconium silicide compound used herein is preferably an oxide,nitride or oxynitride. Similarly, the molybdenum silicide compound usedherein is preferably an oxide, nitride or oxynitride.

In the second embodiment, the preferred phase shift mask blank hasformed on a transparent substrate a phase shift film which is depositedby a reactive sputtering process using a sputtering gas containing anoxygen source gas and/or nitrogen source gas and formed of an oxide,nitride or oxynitride of metal silicide, has a transmittance to exposurelight of several percents to several tens of percents, specificallyabout 3 to about 40%, and provides a phase difference of 180±5 degreesbetween light passing through the phase shifter and light passingthrough only the transparent substrate.

The method of preparing the phase shift film is described in furtherdetail. First, a plurality of targets, a molybdenum silicide target, azirconium silicide target and optionally a silicon target are providedin a single sputtering chamber. Electric discharges are induced to aplurality of targets at the same time for sputtering whereby filmconstituents sputtered from the respective targets are deposited in acombined fashion to achieve a desired film composition (generallyreferred to as co-sputtering). At this point, the substrate is desirablyrotated so that the film constituents from the respective targets areuniformly mixed. A desired compositionally graded layer is obtained byadjusting the powers of electric discharges applied across therespective targets.

Specifically, when it is desired to deposit a layer of molybdenumsilicide oxynitride (MoSiON) on the substrate side, reactive sputteringis preferably carried out using molybdenum silicide as the target and asputtering gas containing nitrogen and oxygen gases as well as argongas.

When it is desired to deposit a layer of zirconium silicide oxynitride(ZrSiON) on the surface side, reactive sputtering is preferably carriedout using zirconium silicide as the target and a sputtering gascontaining nitrogen and oxygen gases as well as argon gas.

In the second embodiment, the MoSiO layer preferably has a composition:Mo=0.2 to 25 at %, Si=10 to 33 at %, and O=33 to 60 at %. The MoSiNlayer preferably has a composition: Mo=0.2 to 25 at %, Si=10 to 42 at %,and N=37 to 57 at %. The MoSiON layer preferably has a composition:Mo=0.2 to 25 at %, Si=10 to 42 at %, O=1 to 60 at %, and N=5 to 57 at %.

Also, the ZrSiO layer preferably has a composition: Zr=0.02 to 25 at %,Si=10 to 33 at %, and O=42 to 67 at %. The ZrSiN layer preferably has acomposition: Zr=0.02 to 25 at %, Si=10 to 33 at %, and N=42 to 67 at %.The ZrSiON layer preferably has a composition: Zr=0.02 to 25 at %, Si=10to 57 at %, O=1 to 60 at %, and N=5 to 57 at %.

In a preferred embodiment wherein a layer of a moderately gradedcomposition is disposed as an intermediate layer between the MoSicompound layer on the substrate side and the ZrSi compound layer on thesurface side, this intermediate layer has an intermediate compositionbetween the composition of the MoSi compound layer on the substrate sideand the composition of the ZrSi compound layer on the surface side. Theterm “moderately graded composition” between two adjacent layers meansthat there may be either a continuous or stepwise transition from thecomposition of one layer to the composition of the other layer. In thelatter case, the term designates at least 5 steps, especially 10 to 50steps of compositional transition from the substrate side to the surfaceside (for example, the Mo amount decreases sequentially in at least 5steps, especially 10 to 50 steps and/or the Zr amount increasessequentially in at least 5 steps, especially 10 to 50 steps).

Such a compositionally graded layer is obtainable by adjusting theelectric discharge powers across the targets. By continuously changingthe electric discharge powers across the targets, a graded layer whosecomposition varies substantially continuously is obtained. By stepwiseor intermittently changing the electric discharge powers across thetargets, a graded layer whose composition varies stepwise is obtained.

Preferably in the second embodiment, the substrate adjacent layer has athickness of 20 to 1,000 Å, especially 40 to 600 Å; and the surfacelayer has a thickness of 20 to 1,000 Å, especially 40 to 600 Å. Thegraded layer has a thickness of 200 to 1,000 Å, especially 300 to 1,000Å and ½ to 1/1, especially 1/1.5 to 1/1 of the thickness of the surfacelayer, in consideration of an ability to adequately control the etchedcross-sectional geometry of the phase shift film.

In the second embodiment, the phase shift mask is arrived at bypatterning the phase shift film of the phase shift mask blank preparedas described above.

Specifically, when a phase shift mask as shown in FIG. 2 is fabricated,a process involving forming a phase shift film 2 on a substrate 1 asdescribed above, then forming a resist film 13 thereon (FIG. 8A),patterning the resist film 13 by lithography (FIG. 8B), etching thephase shift film 2 (FIG. 5C), and thereafter, removing the resist film13 (FIG. 8D) may be employed. Coating and patterning (exposure anddevelopment) of resist film, etching and removal of resist film may beperformed by well-known methods.

Third Embodiment

The third embodiment pertains to a phase shift mask blank comprising asubstrate which is transparent to exposure light and a phase shift filmthereon, the phase shift film having one side contacting the substrateand a surface side remote therefrom, wherein the phase shift filmcomprises a plurality of layers containing a metal and silicon indifferent compositional ratios which are stacked in such order that alayer having a higher etching rate is on the substrate side and a layerhaving a lower etching rate is on the surface side.

Specifically, as shown in FIG. 3, the phase shift mask blank includes atransparent substrate 1 which is transmissive to exposure light such asquartz or CaF₂ and a phase shift film 2 thereon. The phase shift film 2comprises a plurality of layers, two layers 21 and 22 in the illustratedembodiment, containing a metal and silicon in different compositionalratios. The layers are stacked in such order that a layer 21 having ahigher etching rate is on the substrate side and a layer 22 having alower etching rate is on the surface side.

In the third embodiment, the phase shift film comprises a metal silicidecompound such as a metal silicide oxide, metal silicide nitride, metalsilicide oxynitride, metal silicide oxycarbide, metal silicide nitridecarbide or metal silicide oxide nitride carbide. Typically the metal ismolybdenum. Preference is then given to a molybdenum silicide compoundsuch as a molybdenum silicide oxide (MoSiO), molybdenum silicide nitride(MoSiN), molybdenum silicide oxynitride (MoSiON), molybdenum silicideoxycarbide (MoSiOC), molybdenum silicide nitride carbide (MoSiNC) ormolybdenum silicide oxide nitride carbide (MoSiONC).

In the third embodiment, especially where the metal is molybdenum, thatis, where the phase shift film comprises molybdenum silicide compoundsas listed above, the layers in the phase shift film are preferablystacked such that the compositional ratio of silicon to molybdenumincreases from the substrate side to the surface side.

The composition of the molybdenum silicide compound is not particularlylimited. The molybdenum silicide oxide (MoSiO) preferably has acomposition: Mo=1 to 30 at %, Si=25 to 60 at %, and O=30 to 80 at %; andthe molybdenum silicide nitride (MoSiN) preferably has a composition:Mo=1 to 30 at %, Si=25 to 60 at %, and N=30 to 80 at %.

More specifically, for the molybdenum silicide oxynitride (MoSiON), acomposition: Mo=1 to 30 at %, Si=25 to 60 at %, O=1 to 40 at %, and N=1to 60 at % is preferred; for the molybdenum silicide oxycarbide(MoSiOC), a composition: Mo=1 to 30 at %, Si=25 to 60 at %, 0=20 to 70at %, and C=1 to 30 at % is preferred; for the molybdenum silicidenitride carbide (MoSiNC), a composition: Mo=1 to 30 at %, Si=25 to 60 at%, N=20 to 70 at %, and C=1 to 30 at % is preferred; for the molybdenumsilicide oxide nitride carbide (MoSiONC), a composition: Mo=1 to 30 at%, Si=25 to 60 at %, O=1 to 40 at %, N=1 to 60 at %, and C=1 to 30 at %is preferred

In the phase shift mask blank of the third embodiment of the invention,the phase shift film may be a stack of a plurality of phase shift layersformed of different metal compounds.

In the phase shift mask blank of the third embodiment of the invention,it is preferred that a distribution of phase difference (i.e., phasedifference between incident exposure light and light transformed by thephase shifter) in a substrate plane (i.e., at each position whereexposure light is transmitted) at the wavelength of light used forexposure have a center value of 180±10 degrees, and a transmittancedistribution in a substrate plane have a center value of 3 to 40%.Further preferably, the phase difference distribution in a substrateplane is within ±2.0 degrees relative to its center value, and thetransmittance distribution in a substrate plane is within ±0.15%relative to its center value.

In the phase shift mask blank of the third embodiment of the invention,the phase shift film comprises a plurality of stacked layers containinga metal and silicon in which the compositional ratio of silicon to metalis different between layers. Such a phase shift film can be deposited,for example, by sputtering using a metal silicide target. By forming thephase shift film on a substrate which is transparent to exposure light,a phase shift mask blank is manufactured. When layers are deposited instack, the compositional ratio (atomic ratio) of silicon to metal ineach layer of the phase shift film being deposited can be changed byusing, for every layer to be deposited, a metal silicide target having acompositional ratio corresponding to the compositional ratio of siliconto metal in that layer. In the third embodiment, the phase shift maskblank is preferably manufactured by using a sputtering system capable ofsimultaneously causing at least two targets to produce electricdischarges, and sputtering a combination of at least two metal silicidetargets, or a combination of at least one metal silicide target with ametal target or a silicon target or both, thereby depositing layers onthe substrate to form the phase shift film. Specifically, electricdischarges may be induced to a plurality of targets at the same time forsputtering whereby film constituents sputtered from the respectivetargets are deposited in a combined fashion to form a layer of desiredcomposition (generally referred to as co-sputtering). At this point, thesubstrate is desirably rotated by means of a drive mechanism in thesputtering system so that the film constituents from the respectivetargets are uniformly mixed.

In the preferred embodiment using a sputtering system capable ofsimultaneously producing electric discharges on at least two targetswherein a plurality of targets are combined as described above, simplyby setting the input powers across the targets so that the compositionalratio of silicon to metal in each layer of the phase shift film beingdeposited may become a desired value, layers having differentcompositional ratios of silicon to metal can be continuously depositedwithout a need to exchange the targets.

More particularly, when it is desired to increase the compositionalratio of silicon to metal, this can be achieved by increasing the inputpower across a metal silicide target having a higher silicon proportionor a silicon target or by reducing the input power across a metalsilicide target having a lower silicon proportion or a metal target.Similarly, when it is desired to reduce the compositional ratio ofsilicon to metal, this can be achieved by reducing the input poweracross a metal silicide target having a higher silicon proportion or asilicon target or by increasing the input power across a metal silicidetarget having a lower silicon proportion or a metal target. It is alsopossible to effect deposition while achieving a continuous compositionaltransition in each of the layers of the phase shift film.

As to the number of targets used, there may be used one target for eachtarget type having a particular composition or a plurality of targetsfor each target type. In one embodiment, an identical number of targetsare used for all the target types. In another embodiment, only onetarget is used for some target types and a plurality of targets are usedfor the remaining target types.

When a mask pattern is formed by etching, especially reactive ionetching (RIE), the perpendicularity at the boundary between the phaseshift film and the etched-away portion can be adjusted by depositing thephase shift film, in which layers having varying compositional ratios ofsilicon to metal are stacked, by the above-described method. By stackinglayers such that a layer having a higher etching rate is on thesubstrate side and a layer having a lower etching rate is on the surfaceside of the phase shift film, a phase shift mask having goodperpendicularity in etched cross-sectional geometry is obtainable. Thenumber of layers in the phase shift film is not limited to two, andthree or more layers may be included. The upper limit is preferably upto ten layers, though not critical. The composition may be continuouslyvaried to such an extent that no substantially sensible interfacedevelops between layers in a film thickness direction.

The input power across each target is not particularly limited and maybe selected as appropriate as long as targets, especially a metalsilicide target (i.e., a silicon-containing target) and a silicon targetcan produce stable electric discharges. An input power per unit area of0.2 to 20 W/cm² is preferred.

The phase shift mask blank of the third embodiment is manufactured bysputtering targets to deposit layers of the phase shift film. Thetargets used for the deposition of layers of metal silicide or metalsilicide compound are a combination of at least two metal silicidetargets, or a combination of at least one metal silicide target with ametal target or a silicon target or both. Particularly for thedeposition of layers of molybdenum silicide or molybdenum silicidecompound, a combination of at least two molybdenum silicide targets or acombination of at least one molybdenum silicide target with a molybdenumtarget or a silicon target or both is used. Further a metal silicidehaving one or both of oxygen and nitrogen added thereto may be used inorder to maintain a constant composition of layer.

In the third embodiment, a phase shift mask is obtained by patterningthe phase shift film of the aforementioned phase shift mask blank. Thephase shift mask has patterned phase shifters as shown in FIG. 4,wherein first light-transmitting areas (exposed substrate areas) 1 a aredefined between the patterned phase shifters and secondlight-transmitting areas 2 a are provided by the patterned phaseshifters. It is noted that a layer 21 a in FIG. 4 corresponds to thelayer 21 having a higher etching rate in FIG. 3, and a layer 22 a inFIG. 4 corresponds to the layer 22 having a lower etching rate in FIG.3.

Such a phase shift mask may be fabricated by forming a resist pattern onthe phase shift film of the phase shift mask blank by lithography,etching away those portions of the phase shift film which are notcovered with the resist film, and then removing the resist film.

Specifically, when a phase shift mask as shown in FIG. 4 is fabricated,a process involving forming a phase shift film 2 on a substrate 1 asdescribed above, then forming a resist film 13 thereon (FIG. 8A),patterning the resist film 13 by lithography (FIG. 8B), etching thephase shift film 2 (FIG. 8C), and thereafter, removing the resist film13 (FIG. 8D) may be employed. Coating and patterning (exposure anddevelopment) of resist film, etching and removal of resist film may beperformed by well-known methods.

Features Common to First, Second and Third Embodiments

In the first, second and third embodiments of the invention, thesputtering process may employ a direct-current power supply (DCsputtering) or a high-frequency power supply (RF sputtering). Either amagnetron sputtering system or a conventional sputtering system may beused.

The sputtering gas used herein may be an inert gas such as argon, neon,krypton or xenon. The present invention favors reactive sputtering usinga reactive gas. The sputtering becomes reactive sputtering when thereactive gas selected from N₂ gas, ° 2 gas, nitrogen oxide gases such asNO, NO₂ and N₂O, and carbon oxide gases such as CO and CO₂ is used alongwith the inert gas. By adjusting the amount of reactive gas, the phaseshift film deposited is given a desired metal silicide compoundcomposition. The sputtering gases may be introduced into a sputteringchamber by feeding various sputtering gases separately into the chamberor feeding a mixture of some or all sputtering gases and the remaininggases, if any, into the chamber.

Where it is desired to increase the transmittance of a phase shift filmto be deposited, it is recommended that the amounts of oxygen and/ornitrogen-containing gas in the sputtering gas flow be increased so thatmore oxygen and/or nitrogen are taken into the film, or a target havingmore oxygen and nitrogen previously added thereto be used as thesputtering target. It is noted that an excessive content of oxygen canhave negative impacts such as detracting from the chemical resistance ofa phase shift film being deposited or lowering the refractive indexthereof so that a thicker film becomes necessary to accomplish a phaseshift of 180 degrees. Then it is also effective to increase thetransmittance, for example, by increasing the input power across atarget containing a relatively large amount of silicon or a silicontarget for increasing the silicon content in a phase shift film beingdeposited.

In another embodiment, the phase shift mask blank of the invention mayinclude a chromium-base light-shielding film 3 which is formed on thephase shift film 2 as shown in FIG. 5. In yet another embodiment, asshown in FIG. 6, a chromium-base antireflection film 4 may be formed onthe chromium-base light-shielding film 3 for reducing reflection fromthe chromium-base light-shielding film 3. In a still further embodiment,as shown in FIG. 7, a phase shift film 2, a first Cr base antireflectionfilm 4, a Cr base light-shielding film 3, and a second Cr baseantireflection film 4′ are formed on the substrate 1 in order.

The light-shielding film or antireflection film used herein may be achromium base film such as chromium oxycarbide (CrOC) or chromium oxidenitride carbide (CrONC) or a laminate of such films.

The chromium-base light-shielding film or antireflection film may bedeposited by reactive sputtering. Specifically the target used ischromium alone or a compound of chromium combined with oxygen, nitrogenor carbon or a mixture thereof. The sputtering gas used is a mixture ofan inert gas and a reactive gas.

In one example where a CrONC film is to be deposited, the sputtering gasmay be a mixture of at least one carbon-containing gas such as CH₄, Co,and CO, at least one nitrogen-containing gas such as NO, NO₂ and N₂, atleast one oxygen-containing gas such as CO₂, NO and O₂, and an inert gassuch as Ar, Ne, Kr and Xe. The use of CO₂ gas as the carbon and oxygensource gases is especially preferred for uniformity in a substrate planeand ease of control during the deposition process. The sputtering gasesmay be introduced into a sputtering chamber by feeding varioussputtering gases separately into the chamber or feeding a mixture ofsome or all sputtering gases and the remaining gases, if any, into thechamber.

It is preferred that the CrOC film have a composition consistingessentially of 20 to 95 at %, especially 30 to 85 at % of Cr, 1 to 30 at%, especially 5 to 20 at % of C, and 1 to 60 at %, especially 5 to 50 at% of O; and the CrONC film have a composition consisting essentially of20 to 95 at %, especially 30 to 80 at % of Cr, 1 to 20 at %, especially2 to 15 at % of C, 1 to 60 at %, especially 5 to 50 at % of O, and 1 to30 at %, especially 3 to 20 at % of N.

In cases where a chromium-based light-shielding and/or antireflectionfilm is formed on the phase shift film, a phase shift mask on which thechromium-based film 3 remains at the peripheral edges of the substrate 1(see FIG. 9) can be produced by etching away the chromium-based film inthe regions that are necessary for light exposure, thereby leaving thesurface of the phase shift film exposed, then patterning the phase shiftfilm as described above. Alternatively, a phase shift mask can beproduced by applying a resist to the chromium-based film and patterningthe resist, then etching and patterning the chromium-based film and thephase shift film. The regions of the chromium-based film which arenecessary for light exposure are then removed by selective etching so asto leave the phase shift pattern exposed at the surface.

Example

Examples and comparative examples are given below by way ofillustration, and are not intended to limit the scope of the invention.

First Embodiment Example 1

A multilayer film (phase shift multilayer film) was prepared bydepositing alternate layers of molybdenum silicide oxynitride (MoSiON)and silicon oxynitride (SiON).

For the deposition, a dc sputtering system including two targets 33 aand 33 b as shown in FIG. 11 was used. The target 33 a for MoSiON layerswas a MoSi_(3.5) target and the target 33 b for SiON layers was a Sitarget. The sputtering gas was a gas mixture of 20 cm³/min of Ar, 100cm³/min of N₂ and 5 cm³/min Of O₂. A gas pressure of 0.2 Pa was set forsputtering.

While a quartz substrate 1 was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi_(3.5) target forsputtering, depositing MoSiON on the substrate to form a first layer toa thickness of 270 Å. Then the discharge power across the MoSi_(3.5)target was gradually reduced while the discharge power across the Sitarget was gradually increased. The transition process was controlledsuch that the discharge power across the MoSi_(3.5) target became 0 Wand the discharge power across the Si target became 1,000 W at the timewhen the layer reached a thickness of 305 Å from the start of MoSiONdeposition. The transition to deposition of SiON was completed in thisway. The controlled process formed a compositionally graded regionhaving a d/D ratio of 0.1.

Next, the discharge power across the Si target was gradually reduced to0 W while the discharge power across the MoSi_(3.5) target was graduallyincreased to 1,000 W. Subsequently, similar procedures were repeated todeposit layers alternately, eventually producing a multilayer filmhaving four layers in total.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding a satisfactory LER valueof 10 nm.

Example 2

A multilayer film (phase shift multilayer film) was prepared bydepositing alternate layers of molybdenum silicide oxynitride (MoSiON)and silicon oxynitride (SiON).

For the deposition, a dc sputtering system including two targets asshown in FIG. 11 was used. The target for MoSiON layers was a MoSi_(3.5)target and the target for SiON layers was a Si target. The sputteringgas was a gas mixture of 20 cm³/min of Ar, 100 cm³/min of N₂ and 5cm³/min of O₂. A gas pressure of 0.2 Pa was set for sputtering.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi_(3.5) target forsputtering, depositing MoSiON on the substrate to form a first layer toa thickness of 240 Å. Then the discharge power across the MoSi_(3.5)target was gradually reduced while the discharge power across the Sitarget was gradually increased. The transition process was controlledsuch that the discharge power across the MoSi_(3.5) target became 0 Wand the discharge power across the Si target became 1,000 W at the timewhen the layer reached a thickness of 310 Å from the start of MoSiONdeposition. The transition to deposition of SiON was completed in thisway. The controlled process formed a compositionally graded regionhaving a d/D ratio of 0.2.

Next, the discharge power across the Si target was gradually reduced to0 W while the discharge power across the MoSi_(3.5) target was graduallyincreased to 1,000 W. Subsequently, similar procedures were repeated todeposit layers alternately, eventually producing a multilayer filmhaving four layers in total.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding a satisfactory LER valueof 8 nm.

Example 3

A multilayer film (phase shift multilayer film) was prepared bydepositing alternate layers of molybdenum silicide oxynitride (MoSiON)and silicon oxynitride (SiON).

For the deposition, a dc sputtering system including two targets asshown in FIG. 11 was used. The target for MoSiON layers was a MoSi_(3.5)target and the target for SiON layers was a Si target. The sputteringgas was a gas mixture of 20 cm³/min of Ar, 100 cm³/min of N₂ and 5cm³/min of O₂. A gas pressure of 0.2 Pa was set for sputtering.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi_(3.5) target forsputtering, depositing MoSiON on the substrate to form a first layer toa thickness of 190 Å. Then the discharge power across the MoSi_(3.5)target was gradually reduced while the discharge power across the Sitarget was gradually increased. The transition process was controlledsuch that the discharge power across the MoSi_(3.5) target became 0 Wand the discharge power across the Si target became 1,000 W at the timewhen the layer reached a thickness of 203 Å from the start of MoSiONdeposition. The transition to deposition of SiON was completed in thisway. The controlled process formed a compositionally graded regionhaving a d/D ratio of 0.1.

Next, the discharge power across the Si target was gradually reduced to0 W while the discharge power across the MoSi_(3.5) target was graduallyincreased to 1,000 W. Subsequently, similar procedures were repeated todeposit layers alternately, eventually producing a multilayer filmhaving six layers in total.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding a satisfactory LER valueof 9 nm.

Example 4

A multilayer film (phase shift multilayer film) was prepared bydepositing alternate layers of molybdenum (Mo) and silicon (Si).

For the deposition, a dc sputtering system including two targets asshown in FIG. 11 was used. The target for Mo layers was a Mo target andthe target for Si layers was a Si target. Argon was fed at a flow rateof 70 cm³/min as the sputtering gas. A gas pressure of 0.2 Pa was setfor sputtering.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the Mo target for sputtering,depositing Mo on the substrate to form a first layer to a thickness of27 Å. Then the discharge power across the Mo target was graduallyreduced while the discharge power across the Si target was graduallyincreased. The transition process was controlled such that the dischargepower across the Mo target became 0 W and the discharge power across theSi target became 1,000 W at the time when the layer reached a thicknessof 34 Å from the start of Mo deposition. The transition to deposition ofSi was completed in this way. The controlled process formed acompositionally graded region having a d/D ratio of 0.1.

Next, the discharge power across the Si target was gradually reduced to0 W while the discharge power across the Mo target was graduallyincreased to 1,000 W. Subsequently, similar procedures were repeated todeposit layers alternately, eventually producing a multilayer filmhaving 40 layers in total.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding a satisfactory LER valueof 6 nm.

Comparative Example 1

A multilayer film (phase shift multilayer film) was prepared bydepositing layers of molybdenum silicide oxynitride (MoSiON) and siliconoxynitride (SiON).

For the deposition, a dc sputtering system including two targets asshown in FIG. 11 was used. The target for MoSiON layers was a MoSi_(3.5)target and the target for SiON layers was a Si target. The sputteringgas was a gas mixture of 20 cm³/min of Ar, 100 cm³/min of N₂ and 5cm³/min of O₂. A gas pressure of 0.2 Pa was set for sputtering.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi_(3.5) target forsputtering, depositing MoSiON on the substrate to form a first layer toa thickness of 540 Å. Then the discharge power across the MoSi_(3.5)target was gradually reduced while the discharge power across the Sitarget was gradually increased. The transition process was controlledsuch that the discharge power across the MoSi_(3.5) target became 0 Wand the discharge power across the Si target became 1,000 W at the timewhen the layer reached a thickness of 610 Å from the start of MoSiONdeposition. The transition to deposition of SiON was completed in thisway. The controlled process formed a compositionally graded regionhaving a d/D ratio of 0.1. Successively, a second layer was deposited,producing a multilayer film having two layers in total.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding an unsatisfactory LERvalue of 18 nm.

Comparative Example 2

A multilayer film (phase shift multilayer film) was prepared bydepositing alternate layers of molybdenum silicide oxynitride (MoSiON)and silicon oxynitride (SiON).

For the deposition, a do sputtering system including two targets asshown in FIG. 11 was used. The target for MoSiON layers was a MoSi_(3.5)target and the target for SiON layers was a Si target. The sputteringgas was a gas mixture of 20 cm³/min of Ar, 100 cm³/min of N₂ and 5cm³/min of O₂. A gas pressure of 0.2 Pa was set for sputtering.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi_(3.5) target forsputtering, depositing MoSiON on the substrate to form a first layer toa thickness of 300 Å. The system was then switched so that an electricdischarge power of 1,000 W was applied across the Si target forsputtering, depositing SiON to form a second layer. This switchingresulted in a d/D ratio of 0. Layers were alternately deposited bysimilar procedure, producing a multilayer film having four layers intotal.

Line Edge Roughness (LER) Test

On the multilayer film (phase shift multilayer film) produced under theabove-described conditions, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 8B, the phaseshift film (phase shift multilayer film) 2 was dry etched as shown inFIG. 8C, and thereafter, the resist film 13 was removed as shown in FIG.8D. The pattern thus formed was observed. The patterned multilayer filmwas measured for line edge roughness, finding an unsatisfactory LERvalue of 16 nm.

The results of Examples 1 to 4 and Comparative Examples 1 and 2 aresummarized in Table 1. TABLE 1 d/D Layer 1 Layer 2 Number ratio ofThickness Thickness of graded LER No. Composition (Å) Composition (Å)layers region (nm) Example 1 MoSiON 300 SiON 50 4 0.10 10 Example 2MoSiON 300 SiON 50 4 0.20 8 Example 3 MoSiON 200 SiON 33 6 0.10 9Example 4 Mo 30 Si 40 40 0.10 6 Comparative Example 1 MoSiON 600 SiON100 2 0.10 18 Comparative Example 2 MoSiON 300 SiON 50 4 0 16

It is seen from these results that the multilayer films within the scopeof the invention are useful as photomasks by virtue of a fully reducedline edge roughness.

Second Embodiment Example 5

A phase shift multilayer film was prepared using a dc sputtering systemincluding two targets 33 a and 33 b as shown in FIG. 11. The target 33 aused for molybdenum silicide compound layers was a MoSi₄ target and thetarget 33 b used for zirconium silicide compound layers was a ZrSi₆target.

First, sputtering was started by applying an electric discharge power of1,000 W across the MoSi₄ target, depositing a molybdenum silicidecompound on a quartz substrate. As deposition took place, the poweracross the MoSi₄ target was gradually reduced. On the other hand, at thesame time as the start of electric discharge by the MoSi₄ target, agradually increasing electric discharge power was applied across theZrSi, target. The transition process was controlled such that thedischarge power across the MoSi₄ target became 0 W and the dischargepower across the ZrSi₆ target became 500 W at the time when the layerreached a thickness of 700 Å.

The sputtering gas introduced into the system was a gas mixture of 20cm³/min of Ar, 100 cm³/min of N₂ and 5 cm³/min of O₂. A gas pressure of0.2 Pa was set for sputtering. The substrate was rotated at 30 rpm.

The deposition process was terminated when the layer reached a thicknessof 750 Å, obtaining a phase shift film.

It is noted that a rough measure indicative of the molybdenum andzirconium concentrations in the compositions of the substrate adjacentlayer and the surface layer is given by comparing the molybdenum andzirconium concentrations [Mo] and [Zr] in the respective targets. Underthe experimental conditions, [Zr]/[Mo]=0.714.

Chemical Resistance

After one hour immersion in a chemical solution of aqueous ammonia,aqueous hydrogen peroxide and water in a volume ratio of 1:1:10 at 23°C., the blank was measured for transmittance to determine a changethereof. It is believed that those samples having better chemicalresistance show less changes of transmittance before and after thechemical solution immersion. Measurement was made at a wavelength of 193nm. The change of transmittance before and after the chemical solutionimmersion was 0.014.

Steps and Geometry of Etched Cross Section

On the phase shift film (phase shift multilayer film) produced by theabove-described procedure, a resist film 13 was formed as shown in FIG.8A. The resist film 13 was patterned as shown in FIG. 5B, the phaseshift film (phase shift multilayer film) 2 was dry etched with CF₄ basedgases as shown in FIG. 8C, and thereafter, the resist film 13 wasremoved as shown in FIG. 8D.

A cross section of the pattern thus formed was observed to examine thesteps (depicted at 14 in FIG. 13) formed in etched cross section at theinterface between the surface layer 2 b and the lower layer 2 c of thephase shift film. No definite steps were observed.

The etched sidewall in the cross section of FIG. 14 had an angle θ of 86degrees, indicating good perpendicularity.

Example 6

A phase shift multilayer film was prepared using a dc sputtering systemincluding two targets as shown in FIG. 11. The target used formolybdenum silicide compound layers was a MoSi₄ target and the targetused for zirconium silicide compound layers was a ZrSi₄ target.

First, sputtering was started by applying an electric discharge power of1,000 W across the MoSi₄ target, depositing a molybdenum silicidecompound on a quartz substrate. As deposition took place, the poweracross the MoSi₄ target was gradually reduced. On the other hand, at thesame time as the start of electric discharge by the MoSi₄ target, agradually increasing electric discharge power was applied across theZrSi₄ target. The transition process was controlled such that thedischarge power across the MoSi₄ target became 0 W and the dischargepower across the ZrSi₄ target became 500 W at the time when the layerreached a thickness of 650 Å.

The sputtering gas introduced into the system was a gas mixture of 20cm³/min of Ar, 100 cm³/min of N₂ and 5 cm³/min of O₂. A gas pressure of0.2 Pa was set for sputtering. The substrate was rotated at 30 rpm.

The deposition process was terminated when the layer reached a thicknessof 700 Å, obtaining a phase shift film.

It is noted that a rough measure indicative of the molybdenum andzirconium concentrations in the compositions of the substrate adjacentlayer and the surface layer is given by comparing the molybdenum andzirconium concentrations [Mo] and [Zr] in the respective targets. Underthe experimental conditions, [Zr]/[Mo]=1.00.

As in Example 5, chemical resistance was examined, finding a change oftransmittance of 0.009 before and after the chemical solution immersion.With respect to the etched cross section, no definite steps wereobserved. The etched sidewall in cross section had an angle θ of 88degrees, indicating good perpendicularity.

Example 7

A phase shift multilayer film was prepared using a dc sputtering systemincluding two targets as shown in FIG. 11. The target used formolybdenum silicide compound layers was a MoSi₄ target and the targetused for zirconium silicide compound layers was a ZrSi₂₀ target.

First, sputtering was started by applying an electric discharge power of1,000 W across the MoSi₄ target, depositing a molybdenum silicidecompound on a quartz substrate. As deposition took place, the poweracross the Mosi₄ target was gradually reduced. On the other hand, at thesame time as the start of electric discharge by the MoSi₄ target, agradually increasing electric discharge power was applied across theZrSi₂₀ target. The transition process was controlled such that thedischarge power across the MoSi₄ target became 0 W and the dischargepower across the ZrSi₂₀ target became 500 W at the time when the layerreached a thickness of 800 Å.

The sputtering gas introduced into the system was a gas mixture of 20cm³/min of Ar, 100 cm³/min of N₂ and 5 cm³/min of O₂. A gas pressure of0.2 Pa was set for sputtering. The substrate was rotated at 30 rpm.

The deposition process was terminated when the layer reached a thicknessof 850 Å, obtaining a phase shift film.

It is noted that a rough measure indicative of the molybdenum andzirconium concentrations in the compositions of the substrate adjacentlayer and the surface layer is given by comparing the molybdenum andzirconium concentrations [Mo] and [Zr] in the respective targets. Underthe experimental conditions, [Zr]/[Mo]=0.238.

As in Example 5, chemical resistance was examined, finding a change oftransmittance of 0.008 before and after the chemical solution immersion.With respect to the etched cross section, no definite steps wereobserved. The etched sidewall in cross section had an angle θ of 92degrees, indicating good perpendicularity.

Comparative Example 3

A dc sputtering system including two targets as shown in FIG. 11 wasused. This Comparative Example used only MoSi₄ as the target formolybdenum silicide compound.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was applied across the MoSi₄ target for sputtering,depositing a molybdenum silicide compound layer of 500 Å thick on thesubstrate. The sputtering gas introduced into the system was a gasmixture of 20 cm³/min of Ar, 100 cm³/min of N₂ and 5 cm³/min of O₂— Agas pressure of 0.2 Pa was set for sputtering.

As in Example 5, chemical resistance was examined, finding a change oftransmittance of 0.110 before and after the chemical solution immersion,i.e., poor chemical resistance. With respect to the etched crosssection, no steps were observed because of a molybdenum silicide singlelayer film. The etched sidewall in cross section had an angle θ of 76degrees, which is practically less acceptable.

Comparative Example 4

A phase shift multilayer film was prepared using a dc sputtering systemincluding two targets as shown in FIG. 11. A MoSi₄ target was used asthe target for molybdenum silicide compound layers and a ZrSi₄ targetwas used as the target for zirconium silicide compound layers.

While a quartz substrate was rotated at 30 rpm, an electric dischargepower of 1,000 W was first applied across the MoSi₄ target forsputtering, depositing a first layer of 500 Å thick on the substrate.The sputtering gas introduced into the system was a gas mixture of 20cm³/min of Ar, 100 cm³/min of N₂ and 5 cm³/min of O₂. A gas pressure of0.2 Pa was set for sputtering.

Next, an electric discharge power of 500 W was applied across the ZrSi₄target for sputtering, depositing a second layer of 200 Å thick. Thedepositing conditions were the same as used for the first layer.

It is noted that a rough measure indicative of the molybdenum andzirconium concentrations in the compositions of the substrate adjacentlayer and the surface layer is given by comparing the molybdenum andzirconium concentrations [Mo] and [Zr] in the respective targets. Underthe experimental conditions, [Zr]/[Mo]=1.000.

As in Example 5, chemical resistance was examined, finding a change oftransmittance of 0.014 before and after the chemical solution immersion.With respect to the etched cross section, steps of about 4 nm wereobserved. The etched sidewalls in cross section for each layer wereinclined, and in the most inclined areas, had an angle θ of 78 degrees,which is practically less acceptable.

The results of Examples 5 to 7 and Comparative Examples 3 and 4 aresummarized in Table 2. TABLE 2 [Zr]/[Mo] 1st 2nd (target layer layerLayer composition θ Chemical No. Target Target configuration ratio)(deg) resistance Example 5 MoSi₄ ZrSi₆ graded 0.714 86 0.014 Example 6MoSi₄ ZrSi₄ graded 1.000 88 0.009 Example 7 MoSi₄ ZrSi₂₀ graded 0.238 920.008 Comparative Example 3 MoSi₄ 1 layer — 76 0.110 Comparative Example4 MoSi₄ ZrSi₄ 2 layers 1.000 78 0.014

According to the invention, in a phase shift mask blank having a phaseshift film of two or more layers on a transparent substrate, the phaseshift film has a zirconium silicide compound-based composition on asurface side and a molybdenum silicide compound-based composition on asubstrate side, and includes at least one layer of a moderately gradedcomposition. There are thus provided a phase shift mask blank and aphase shift mask which exhibit an improved etched cross-sectionalgeometry following mask pattern formation and good chemical resistancewhile satisfying optical properties.

Third Embodiment Example 8

A dc sputtering system as shown in FIG. 15 was used comprising a cathodestructure having four targets 33 and a drive mechanism for rotating asubstrate 1 about its axis in a chamber 31. An inlet 34 is provided forfeeding a sputtering gas into the chamber 31. The targets included twoMoSi_(3.66) targets (sputtering face area 38 cm²) and two Si targets(sputtering face area 38 cm²). The sputtering gas used was a mixture ofAr, N₂ and N₂O, which was fed as shown in Table 3. While rotating asquare quartz substrate of 152 mm on each side and adjusting the inputpowers across the targets as shown in Table 3, a phase shift filmconsisting of two molybdenum silicide oxynitride layers having differentcompositional ratios of silicon to molybdenum was deposited on thesubstrate. TABLE 3 Target No. Sputtering gas 1 2 3 4 (flow rate, sccm)Target composition Ar N₂ N₂O MoSi_(3.66) MoSi_(3.66) Si Si Upper layer 520 0.5 Input 130 W 52 W 150 W 250 W (surface side) power Lower layer 520 2.2 Input 194 W 70 W 150 W 250 W (substrate side) power

In a 142 mm×142 mm region of the phase shift film as deposited excludinga peripheral rim, a phase shift and a transmittance at the wavelength193 nm were measured, finding a phase shift of 178.84±1.57 degrees and atransmittance of 5.65+0.09%. These data prove that the phase shift filmhas a phase shift distribution within ±2.0 degrees and a transmittancedistribution within ±0.15%. The film was 690 Å thick. For measurement ofphase difference and transmittance, a phase shift measurement systemMPM-193 by Lasertec Corp. was used.

The composition of the phase shift film thus deposited was analyzed in adepth direction by XPS, with the results shown in FIG. 16. Since theinput powers across the MoSi targets were changed between the upperlayer (on the surface side) and the lower layer (on the substrate side),the compositional ratio of Si to Mo was 5.71 for the upper layer and4.86 for the lower layer. It is evident that the compositional ratio ofsilicon to metal was different between the upper and lower layers.

From the phase shift mask blank fabricated above, a phase shift mask wasmanufactured by effecting reactive ion etching (RIE) according to themask patterning procedure as shown in FIG. 8. A substantiallyperpendicular sidewall appeared at the interface between the phase shiftfilm and the etched-away portion, indicating good perpendicularity inetched cross-sectional geometry.

Comparative Example 5

A dc sputtering system as shown in FIG. 15 was used comprising a cathodestructure having four targets and a drive mechanism of rotating asubstrate about its axis in a chamber. The targets included four MoSi₉targets (sputtering face area 38 cm²). As the sputtering gas, N₂, N₂Oand CO were fed at a flow rate of 40, 0.6 and 1.0 sccm, respectively.While rotating a square quartz substrate of 152 mm on each side andsetting the input powers across the targets as shown in Table 4, a phaseshift film in the form of a single molybdenum silicide oxide nitridecarbide layer was deposited on the substrate. TABLE 4 Target No. 1 2 3 4Target composition MoSi₉ MoSi₉ MoSi₉ MoSi₉ Input power 220 W 220 W 150 W150 W

In a 142 mm×142 mm region of the phase shift film as deposited excludinga peripheral rim, a phase shift and a transmittance at the wavelength193 nm were measured, finding a phase shift of 179.23±1.26 degrees and atransmittance of 6.19±0.13%. The film was 790 Å thick.

The composition of the phase shift film thus deposited was analyzed in adepth direction by XPS, with the results shown in FIG. 17. Since thesingle molybdenum silicide oxide nitride carbide layer was depositedusing only molybdenum silicide targets, the compositional ratio of Si toMo was kept constant.

From the phase shift mask blank fabricated above, a phase shift mask wasmanufactured by effecting reactive ion etching (RIE) according to themask patterning procedure as shown in FIG. 8. A footing on the substrateside appeared at the interface between the phase shift film and theetched-away portion, indicating inferior perpendicularity in etchedcross-sectional geometry to Example 8.

1. A phase shift mask blank comprising a substrate which is transparentto exposure light and a phase shift film thereon, said phase shift filmhaving one side contacting the substrate and a surface side remotetherefrom, said phase shift film comprising a plurality of layerscontaining a metal and silicon in different compositional ratios whichare stacked in such order that a layer having a higher etching rate ison the substrate side and a layer having a lower etching rate is on thesurface side.
 2. The phase shift mask blank of claim 1 wherein saidphase shift film comprises one of metal silicide oxide, metal silicidenitride, metal silicide oxynitride, metal silicide oxycarbide, metalsilicide nitride carbide and metal silicide oxide nitride carbide. 3.The phase shift mask blank of claim 1 wherein said metal is molybdenum.4. The phase shift mask blank of claim 3 wherein in said phase shiftfilm, the plurality of layers are stacked such that the compositionalratio of silicon to molybdenum increases from the substrate side to thesurface side.
 5. The phase shift mask blank of claim 1 wherein a phasedifference distribution in a substrate plane at the wavelength of lightused for exposure has a center value of 180±10 degrees, and atransmittance distribution in a substrate plane has a center value of 3to 40%.
 6. The phase shift mask blank of claim 5 wherein the phasedifference distribution in a substrate plane at the wavelength of lightused for exposure is within ±2.0 degrees relative to its center value,and the transmittance distribution in a substrate plane is within ±0.15%relative to its center value.
 7. A method for manufacturing the phaseshift mask blank of claim 1, comprising using a sputtering systemcapable of simultaneously causing at least two targets to produceelectric discharges, and sputtering a combination of at least two metalsilicide targets, or a combination of at least one metal silicide targetwith a metal target or a silicon target or both, thereby depositinglayers on the substrate to form the phase shift film.
 8. The method ofclaim 7 wherein the sputtering is reactive sputtering using a reactivegas, and said phase shift film comprises one of metal silicide oxide,metal silicide nitride, metal silicide oxynitride, metal silicideoxycarbide, metal silicide nitride carbide and metal silicide oxidenitride carbide.
 9. The method of claim 7 wherein said metal ismolybdenum.
 10. The method of claim 9 wherein in said phase shift film,the plurality of layers are stacked such that the compositional ratio ofsilicon to molybdenum increases from the substrate side to the surfaceside.
 11. A phase shift mask fabricated by patterning the phase shiftfilm of the phase shift mask blank of claim
 1. 12. A method formanufacturing a phase shift mask, comprising forming a resist filmpattern on the phase shift film of the phase shift mask blank of claim 1by lithography, etching away those portions of the phase shift filmwhich are not covered with the resist film, and removing the resistfilm.